1. Field of the Invention
The present invention relates to a method for detecting an unbalanced drum in a drum type washing machine, and more particularly, to a method for detecting whether a drum is unbalanced or not by checking for deviations in the number of revolutions of the drum.
2. Prior Art
FIG. 1 is a perspective view of a conventional drum type washing machine, and FIG. 2 is a schematic view of a device for detecting unbalanced drum in the drum type washing machine shown in FIG. 1. The drum type washing machine has a body 1, a tub 2 supported in the body 1 by a suspension and a shock absorber which are not shown, and a drum 3 installed in the tub 2 to be capable of rotating.
A driving motor 5 for driving the drum 3 is installed at one side of the tub 2, and a door 8 for opening/closing the tub 2 is installed on the front of the body 1. At the upper front area of the body 1, a control panel 10 is provided, through which a user controls the operation of the washing machine.
A power transmission 20 is provided in the rear of the tub 2. The power transmission 20 is comprised of pulleys 21 and 22 which are respectively assembled with the drum 3 and the driving motor 5, and a belt 23 for connecting the pulleys 21 and 22 with each other. As the driving motor 5 operates, the drum 3 is rotated through the power transmission 20. Meanwhile, the washing machine has a tachometer 50 for gauging the number of revolutions of the drum 3.
The operations of the washing machine consists of a washing operation, a rinsing operation, and a dehydrating operation. In order to perform the washing operation, the user opens the door 8 and puts laundry into the drum 3, and then utilizes the control panel 10. The control part 40 in the washing machine controls the operation of the washing machine according to the operation by the user.
In the washing operation, the laundry is washed while the drum 3 is rotated by the driving motor 5. That is, as the drum 3 is rotated, the laundry in the drum 3 is raised by the drum 3 and then is dropped. The washing operation of detergent is performed by the impact applied to the laundry in such a situation. The drum 3 is rotated in forward and reverse directions alternately.
Meanwhile, in the dehydrating operation, the driving motor 5 rotates the drum 3 in a high rotational velocity. The laundry is dehydrated by the centrifugal force generated by the rotating drum 3.
Since the drum 3 is rotated at a high rotational velocity during the dehydrating operation, vibrations of the drum 3 may occur. In particular, if the unbalance of the drum 3 caused by the uneven distribution of the laundry in the drum 3 occurs, the vibrations can become great. Such vibrations may cause a significant malfunction in the dehydrating operation, and the operation of the washing machine can be stopped if the vibrations are excessive. Therefore, the washing machine detects the unbalanced drum 3, and performs a balancing operation if an unbalanced drum 3 is detected.
FIG. 3 shows a conventional method for detecting an unbalanced drum.
At first, the tachometer 50 detects S101 pulse signals such as pulse width or pulse period according to the rotation of the driving motor 5. The detection of the pulse signals is continued S102 at predetermined time periods. The pulse signals detected by the tachometer 50 are input to the control part 40.
The control part 40 judges S103 whether the drum 3 has become unbalanced or not, with an unbalance detection program which has been programmed therein. If the drum 3 has been detected as being unbalanced, a balancing operation is performed S104, and if the drum 3 has been detected as being balanced, the dehydrating operation is performed S105.
The balancing operation is performed by rotating the drum 3 in bilateral rotational directions alternately. Then, the laundry in the drum 3 is distributed evenly, hence the drum 3 becomes balanced. After the balancing operation, the above-described process is repeated.
However, in such a conventional method for detecting an unbalanced drum in a drum type washing machine, the control part 40 must accumulate the pulse signals during a predetermined time period in order to detect the unbalance, so the time required in detecting the unbalance is long. Furthermore, in order to detect an unbalanced drum on the basis of the accumulated pulse signals, an additional unbalance detection program has to be provided, and a lot of time is additionally consumed in performing such unbalance detection program. Therefore, the dehydrating operation and the balancing operation cannot be completed in a short time, and the time consumed for the operation of the washing machine is lengthened.